the 6LU8 is like a 6V6 and 1/2 of 12AT7 placed in s single 12 pin compactron envelope, i wanted to use the 21LR8 at first but then the novar sockets had issues, they were loose, i found out that they were intended for tubes like the PL504 which had thicker pins.....oh well.....here is the link for the 6LU8: http://frank.pocnet.net/sheets/123/6/6LU8.pdf

so i designed all the irons needed, the power transformers, filter choke and output transformers, the 2 output transformers used Edrel's RM20 cores which like his more expensive Z11's had the same 0.35mm thikness, Deeco Irons were then used for the power transformers and filter choke, deeco iron has a thickness of 0.5mm....

pics of the irons and some parts:

the power supply used the 3DG4 tube,http://frank.pocnet.net/sheets/093/3/3DG4.pdf it is likewise a hybrid rectifier using solid-state bridge, a toggle selector switch is used to select ss only rectification if desired.....the advntage of a hybrid is that being a full bridge rectifier transformer heating is way much lower than if staright full-wave is used using tube rectifier only......design and construction of the power transformer then becomes easier and cheaper....

construction pics:

testing:

i used another set of speakers to test whether the polarity of the output transformer was correct, there is a 50-50 chance you will get it, but upon power up motorboating happened so i had to power down and reverse the plate lead connections to the right one.....after that, the amps was dead quiet, no hum, no hiss no noise.....i tested the amp and found out that the sensitivity was quite low, so i hooked up the 7N7 preamp to get a more decent volume.....later on i found out that i connected 470ohms feedback resistor instead of 4.7k so gain was really low....

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the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....

Cool project! Those TV tubes are nice; imagine that: a stereo PP amp with just four tubes. Even though it's usually not easy to find the output iron (I wasn't surprised to see you made custom designs), they're nice to tinker with.

But let me get this straight: you got 700 of these tubes? So we can expect a manufacturing output of another 174 of those amplifiers you showcase here?

Cool project! Those TV tubes are nice; imagine that: a stereo PP amp with just four tubes. Even though it's usually not easy to find the output iron (I wasn't surprised to see you made custom designs), they're nice to tinker with.

But let me get this straight: you got 700 of these tubes? So we can expect a manufacturing output of another 174 of those amplifiers you showcase here?

thanks to YvesM, i used his design in winding the output transformer, it has around 10k primary anode to anode resistance to 6 ohms secondary....

those 700 tubes are not all same types, although i have around 40 or so 6LU8 and 21LR8 tubes to play around with......the rest are tv horizontal sweep tubes, damper diodes, and odd voltage double triodes, pentodes etc., etc..

i am not scared of non-6 volt tubes, i can make traffos for then as needed....

so far i have finished 2 albums listening to this amp, first is Beatles' "Rubber Soul" my all time favorite, and Norah Jones' "com away with me." .......very enjoyable listening....

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the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....

There are two types of 9-pin compactron sockets, novar and magnoval. the pin pattern is the same, but magnoval based tubes have thicker pins. The loose-fitting ones you tried were probably magnoval. Novar sockets are only NOS and getting very hard to find.

per CompactronTubesIndex.shtml:
...Every so often I hear talk of "9-pin Compactrons." Technically those don't exist; all Compactron tubes have 12 pins....However, in 1962 RCA introduced a line of tubes called Novar. These are all-glass tubes with nine .038" (1.2mm) pins on a base larger than that of the familiar 9-pin miniature. RCA introduced them for use in audio equipment, and the motivation may have been to create a larger base and bulb for greater power dissipation. Most of the Novars I've seen have been power pentodes like the 7868, or color TV rectifiers. There's something to careful of with Novar tubes. A very similar line was introduced in Europe at about the same time. These were called Magnoval tubes, and they have nine pins on the same diameter circle. However, and crucially, Magnoval tubes have larger pins, at .046" (1.27mm). If you plug a Magnoval tube into a Novar socket, the larger pins will damage the pin contacts on the socket. You can wreck the socket of a late-era tube tester by trying to test a Magnoval in the Novar socket. Before you test what you think is a Novar tube, put a mic or a digital caliper on those pins!

There were not as many Novar tubes as Compactrons, and they were never very popular. Sockets are more difficult to find, though I've seen them online. Sellers sometimes claim that a single socket will work for both Novar and Magnoval, but that's not true. The larger Magnoval pins will damage any socket designed for Novar tubes, and Novar tubes will rattle around in any socket designed for Magnoval pins.